[GSS](7.1.z) HHH-12740 Subselect fetching doesn't work when multiLoad was used

Given some entities loaded into the session via MultiIdentifierLoadAccess.multiLoad() in one batch via a query using an in-clause. These entities have lazy-fetched OneToMany associations annotated with FetchMode.SUBSELECT.
When accessing these associations, they will be fetched using one query per parent entity, just as if the parent entities had been loaded one by one.
This creates serious performance issues when using multiLoad as a replacement for directly querying multiple IDs, which we did do utilize 1st level cache.